Here is an interesting article from the UC Berkeley News Center that came out a couple of weeks ago that talks about how in-law/secondary units could be a great way to help accommodate the projected population growth via dealing with infill development in communities throughout the region.  They are currently looking into regulatory challenges, such as parking restrictions, but are hoping that this study will help mobilize the market for secondary units and lead the way to boost the East Bay affordable housing stock inventory.

http://newscenter.berkeley.edu/2011/09/13/in-law-units-east-bay/